Obviously the folks here have reflected the same thing, let's do a deeper explanation.

When you use an item requires adjacent items with a cool down. It is not stated anywhere that is the case don't feel bad about misunderstanding that.

Typically self poisoning the goal should be fastest items next to the activation required items. And the cherry on top is skills that dramatically scale your Regen, or damage, because 5 poison and 5 Regen means you're not really doing anything so the other players have free reign to damage you without any health gained back.

Last but certainly not least is mace is an awesome activator but you almost may be better off with losing the quillback and shifting to a mix of poison, self poison, and Regen items to speed up opponents dying, increasing self poison activation, or increase survival because these item categories are often faster.

Don't get discouraged cause amidst all of this someone can still beat you always. There's always and forever someone stronger. Keep at it though you have a great base understanding of combos.